*3.2.9. Host resistance*

have previously been infected with coccidiosis infections. On the day of vaccination, the birds should be closely monitored. The apparent health of flock should be analyzed. Moreover, the color and consistency of fecal droppings, abnormal sounds from birds, respiratory distress, etc. should be evaluated. After being satisfied with the proper health status of the bids, the

Nutrition plays a significant role in the development and function of the immune system [42]. The commercial feed offered to poultry should be analyzed regularly and the level of toxins be checked on a regular basis. Especially in summer and humid environment conditions, the fungus grows on feed ingredients and fungal metabolites gain entry into the body of poultry, and as a result, they cause immune-suppression, decreased growth, hypersensitivity

In poultry birds, age is considered for the vaccination of bird; receptors for different pathogens develop in the body of poultry bird at specific ages, so the vaccination is done keeping in view the age of the bird, that is, ND + IB vaccine is done on the first day of birth. Similarly, the Marek's disease vaccine is done immediately after hatching of chicks in the hatchery machine. The IBD (infectious bursal disease/Gumboro) vaccine is done at 10–12 days of birth and booster is given after 10 days. In broiler birds, the hydropericardium syndrome (HPS)/ Angara vaccine is done at 21–23 days of birth. So, the age of the bird is very important for vaccination. The domestic/rural poultry requires injection of ND after every 2–2.5 months.

As the breeder/parent flocks of poultry are routinely vaccinated against viral diseases which are prevalent in the area, the newly hatched chicks have maternal antibodies in their blood. It is suggested that the bird should be a minimum 11 days old at the time of administration of

In Pakistan, the outbreak of diseases like infectious bronchitis and avian influenza occurs in birds during winter; for that purpose, the birds must be vaccinated prior to winter, so that proper antibody titer may be reached in birds before exposure to the disease causing virus or bacteria in birds. To avoid any economic loss, a record may be maintained and a strict vaccination schedule according to disease prevalence in the area must be followed in poultry

The poultry flocks are properly prepared for administration of oral vaccines. The birds are offered feed and are kept off water for 2 h before administration of vaccines. The drinkers

IBD vaccine and 7 days old at the time of administration of ND vaccine [31].

concerned staff may be allowed to vaccinate the flock.

88 Immunization - Vaccine Adjuvant Delivery System and Strategies

*3.2.4. Balanced feed*

and decreased feed intake.

*3.2.6. Consideration of maternal antibodies*

*3.2.7. Proper vaccination schedule*

*3.2.8. Preparation of flocks for vaccination*

flocks [43].

*3.2.5. Maturity of bird*

Certain genes are discovered which have genetic resistance against viral diseases of poultry [44]. The breeding for disease resistance may provide good long-term solutions for disease control [45]. However, the emergence of new genetic groups and mutations require new vaccine practices for successful immunization [46].
